explain to me the ending of season 2 episode 20:

Caroline was rescued by Damon from being sacrificed in the ritual, along with Tyler. Damon tells klaus what he did and that he can kill him, he doesn't care. Klaus replies that if he's learned something over the thousand years he's been trying to break the curse, it is to always have a backup. I think at this point it's pretty clear that without Tyler Klaus was going to sacrifice Jules. The thing is that when Damon completes the line and says "backup vampire" Klaus says "I've got that covered" and attacks Damon, and I thought, I think we all did, that he was using Damon to replace Caroline. When we see Damon recovering, Katherine is by his side and tells him that Klaus said Damon was "as good as dead" because Klaus knew about the werewolf bite, which means Damon is kind of already dying(the vampire bitten by a werewolf is a goner).
Seeing as how the vampire he was gonna use escaped (Caroline) and the other one he was gonna use has a werewolf bite and is dying (Damon), Klaus needs another vampire. And that's when the Jenna thing comes, Klaus wants to use her as the vampire to be sacrificed in the ritual. He made Katherine call her and Kat had no choice because if she didn't do it Klaus would've found out she was on vervain and then Katherine would be dead for good.
To become a vampire you have to die with vampire blood on your system, when you wake up you're on transition and to become a "full-on" vampire you have to drink human blood or you die for good. Jenna's human life is gone, she's dead but in transition, she has to complete the process and then she's supposed to be sacrificed.

I wrote a lot and I don't know if it actually helps you to understand or made it worse but I tried my best.

Jenna is in transition: or she died or became vampire. Because Tyler bite Damon, and know he'll die, just like Rose(but i dont belive damon die,because they arent crazy)

i'm completely overwhelmed by Jenna's situation! She found out Vamps were real like a few days ago in TVD time and now she's in transition?? WTFF
And poor Damon. (He's not going to die cuz he's like everybody's fav character) He's going to have dementia and go crazyy and have that nasty thing spread all over his arm :(